This invention relates to improvements in heat fusing apparatus and more particularly to heat fusing apparatus in which a heated element is brought into contact with an image formed of a resinous powder to heat the powder and fix the powder image to a sheet of paper.
Contact fusing apparatus is known in the prior art. However, contact fusing has the disadvantage that "offset" may occur. Offset is caused by part of the image sticking to the surface of the contact fusing device so that when the next sheet comes into contact with the fusing device the image partially removed from the first sheet is transferred to the second sheet. This offset problem has been overcome in commercial machines by fabricating the outer surface of the heated roll with a material such as Teflon. However, this apparatus requires that the heated roll be continuously coated with an offset preventing liquid such as silicone oil during operation. There has been developed a heated roll coated with a resilient material such as silicone rubber which when operated with a deformable backup roll will produce offset-free operation over a particular range of temperature and pressure without the use of an offset preventing liquid such a silicone oil. Such a system is described in U. S. Pat. No. 3,666,247 issued May 30, 1972, and assigned to the same assignee as this application. This apparatus successfully solved the offset problem without using silicone oil. However, the resultant coating on the fusing roll disclosed therein has not had sufficient useful life so that it is suitable for use in a system which utilizes high process speeds in which the components of the system are required to have maintenance-free operation for a long period of time. Other silicone rubbers with properties which would indicate a longer useful life in the fuser environment were tried using prior art curing techniques. While some improvement was achieved, the useful life remained well below that required. The conventional prior art curing process for silicone rubbers involves the use of a curing agent such as certain of the peroxides and it was discovered that the curing agent produces several undesirable side effects in thin sections of silicone rubber so that these rubbers have both reduced and variable lives in the fusing environment.